1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for etching an anti-reflective coating (ARC) film.
2. Discussion of the Related Art
To keep up with the increase in device packing density, the tendency is toward a lower critical dimension (CD). CDs are 0.8 .mu.m for a 1 Mb device, 0.35 .mu.m for a 64 Mb device, 0.25 .mu.m for a 256 Mb device, and 0.18 .mu.m for a 1 Gb device.
Thus, when using an exposure method for patterning, deep ultraviolet (DUV) is being preferred to i-line. For the future, an exposure method employing X-rays is expected to be preferred.
An aromatic polysulfone structure for a general organic anti-reflective coating film is as follows: ##STR1## An anti-reflective coating (ARC) film with a constituent having the above-described aromatic polysulfone structure used in DUV microlithography.
In general, a bottom anti-reflective coating (BARC) is divided into organic constituents and inorganic constituents. Like photoresist, an ARC film of organic constituents contains constituents such as C, H, and O, and has a high viscosity. An ARC of inorganic constituents is mainly composed of elements in the SiO.sub.2 system or the carbon (C) system.
A conventional method for etching an ARC film will be discussed with reference to the attached drawings. FIGS. 1a through 1c show the steps of a method for etching an organic ARC film. Referring initially to FIG. 1a, on a semiconductor substrate 1 there is formed an etching layer 2 which will be selectively etched. Next, an organic anti-reflective coating (ARC) film 3 is formed on the etching layer 2. Subsequently, a photoresist layer 4 is formed on the organic ARC film 3, and then patterned through exposure and development.
Thereafter, as shown in FIG. 1b, a down-stream type of etching process is performed by using O.sub.2 plasma with the addition of N.sub.2 or gases such as CHF.sub.3, CF.sub.4, or C.sub.2 F.sub.6, which contain all fluorine (F). Otherwise, a reactive ion etching (RIE) process or an etching process using magnetic enhanced reactive ion etching (MERIE) equipment is performed. In this case, polymers 4a such as CN.sub.x, CHF.sub.x, or CF.sub.x are formed on both sides of the organic ARC film 3 beneath the photoresist layer 4. A loss of the upper portions of the photoresist layer 4 also takes place as shown in FIG. 1b.
When the thickness of the photoresist layer 4 having undergone erosion due to etching is designated "b" and the thickness of an effective mask (i.e., thickness of the photoresist layer 4 which did not undergo erosion and the ARC film 3) is designated "a", the value of a/b is very tiny.
Referring to FIG. 1c, after the removal of the photoresist layer 4, the etching layer 2 is selectively removed with the organic ARC film 3 serving as a mask, thereby completing the conventional etching process.
The conventional method for etching an ARC film has disadvantages. Since, in proportion to a very low value of a/b, the thickness of the portion of the photoresist layer serving as the effective mask is very small, the photoresist layer poorly serves as a mask to etch an etching-objective layer.